1. Field of the Invention
This invention relates to a photodetector of semiconductor material, and especially but not exclusively to an infrared photodetector.
2. Discussion of Prior Art
Semiconducting infrared detectors are well known, such as for example those of cadmium mercury telluride (CMT). They are normally operated in an extrinsic regime in which the equilibrium majority carrier concentration greatly exceeds the intrinsic carrier concentration. To achieve this, CMT detectors sensitive in the 8-12 .mu.m and 3-5 .mu.m wavelength intervals are normally cooled to about 80.degree. K. and 200.degree. K. respectively. One advantage of this is that responsivity is high because a large fractional change in carrier density results from exposure to infrared radiation. Moreover, the signal-to-noise ratio is high because the noise due to fluctuations in the equilibrium carrier density is low. This noise benefit is particularly significant with respect to Auger generation-recombination processes. In these the principal process is electron-hole pair production by electron-impact ionisation, the ionising electrons having thermal energy greater than the relevant semiconductor band gap.